The general goal of this proposal is to understand how non-synaptic types of interaction present in the mammalian nervous system can modify embriologically determined properties of the neuron. The two models chosen for this study are the motoneuron terminals and the spinal ganglion cells. The idea is to analyze these neural structures in vivo and in relative isolation, i.e. without the muscle and peripheral receptor apparatus respectively. This can be achieved by studying the properties of growing axons, be they sensory or motor, at various times after section of a peripheral nerve. In this experimental situation the different factors controlling acetylcholine release by growing motor terminals and the transducer properties of growing sensory fibers will be studied. By comparison with the known physiological mechanisms present in the normal situation (neuromuscular junction and peripheral receptor) the degree and type of cellular interaction will be established. The study of the physiological properties of growing axons in vivo should bring a much needed insight into the mechanisms of peripheral pain syndromes due to nerve injury (e.g. causalgia and painful amputation neuroma).